New lipid-modifying therapies

Applications of fluorine to the construction of bioisosteric elements for the purposes of novel drug discovery

Introduction There continues to be an exponential rise in the number of small molecule drugs that contain either a fluorine atom or a fluorinated fragment. While the unique properties of fluorine enable the precise modulation of a molecule's physicochemical properties, strategic bioisosteric replacement of fragments with fluorinated moieties represents an area of significant growth.Areas covered This review discusses the strategic employment of fluorine substitution in the design and development of bioisosteres in medicinal chemistry. In addition, the classic exploitation of trifluoroethylamine group as an amide bioisostere is discussed. In each of the case studies presented, emphasis is placed on the context-dependent influence of the fluorinated fragment on the overall properties/binding of the compound of interest.Expert opinion Whereas utilization of bioisosteric replacements to modify molecular structures is commonplace within drug discovery, the overarching lesson to be learned is that the chances of success with this strategy significantly increase as the knowledge of the structure/environment of the biological target grows. Coupled to this, breakthroughs and learnings achieved using bioisosteres within a specific program are context-based, and though may be helpful in guiding future intuition, will not necessarily be directly translated to future programs. Another important point is to bear in mind what implications a structural change based on a bioisosteric replacement will have on the candidate molecule. Finally, the development of new methods and reagents for the controlled regioselective introduction of fluorine and fluorinated moieties into biologically relevant compounds particularly in drug discovery remains a contemporary challenge in organic chemistry.

Human pluripotent stem cells for modelling human liver diseases and cell therapy

The liver is affected by many types of diseases, including metabolic disorders and acute liver failure. Orthotopic liver transplantation (OLT) is currently the only effective treatment for life-threatening liver diseases but transplantation of allogeneic hepatocytes has now become an alternative as it is less invasive than OLT and can be performed repeatedly. However, this approach is hampered by the shortage of organ donors, and the problems related to the isolation of high quality adult hepatocytes, their cryopreservation and their absence of proliferation in culture. Liver is also a key organ to assess the pharmacokinetics and toxicology of xenobiotics and for drug discovery, but appropriate cell culture systems are lacking. All these problems have highlighted the need to explore other sources of cells such as stem cells that could be isolated, expanded to yield sufficiently large populations and then induced to differentiate into functional hepatocytes. The presence of a niche of “facultative” progenitor and stem cells in the normal liver has recently been confirmed but they display no telomerase activity. The recent discovery that human induced pluripotent stem cells can be generated from somatic cells has renewed hopes for regenerative medicine and in vitro disease modelling, as these cells are easily accessible. We review here the present progresses, limits and challenges for the generation of functional hepatocytes from human pluripotent stem cells in view of their potential use in regenerative medicine and drug discovery.

Meta-analysis of the effect of nicotinic acid alone or in combination on cardiovascular events and atherosclerosis

OBJECTIVE

High-density lipoprotein cholesterol (HDL-C) concentration is a strong predictor of cardiovascular events in both naïve and statin-treated patients. Nicotinic acid is an attractive option for decreasing residual risk in statin-treated or statin-intolerant patients since it increases HDL-C by up to 20% and decreases low-density lipoprotein cholesterol and lipoprotein(a) plasma concentrations.

METHODS

We performed a computerized PubMed literature search that focused on clinical trials evaluating niacin, alone or in combination with other lipid-lowering drugs, published between January 1966 and August 2008.

RESULTS

Among 587 citations, 29 full articles were read and 14 were eligible for inclusion. Overall 11 randomized controlled trials enrolled 2682 patients in the active group and 3934 in the control group. In primary analysis, niacin significantly reduced major coronary events (relative odds reduction=25%, 95% CI 13, 35), stroke (26%, 95% CI=8, 41) and any cardiovascular events (27%, 95% CI=15, 37). Except for stroke, the pooled between-group difference remained significant in sensitivity analysis excluding the largest trial. In comparison with the non-niacin group, more patients in the niacin group had regression of coronary atherosclerosis (relative increase=92%, 95% CI=39, 67) whereas the rate of patients with progression decreased by 41%, 95% CI=25, 53. Similar effects of niacin were found on carotid intima thickness with a weighted mean difference in annual change of -17 microm/year (95% CI=-22, -12).

CONCLUSIONS

Although the studies were conducted before statin therapy become standard care, and mostly in patients in secondary prevention, with various dosages of nicotinic acid 1-3g/day, this meta-analysis found positive effects of niacin alone or in combination on all cardiovascular events and on atherosclerosis evolution.

Novel patent publications on high-affinity nicotinic acid receptor agonists

BACKGROUND

Nicotinic acid (NA) has been used as a drug to treat dyslipidemia for > 50 years. In outcome clinical trials, NA displayed remarkable efficacy in patients with cardiovascular diseases by modifying lipid profiles that results in reduced morbidity and mortality. On the other hand, NA induces vasodilation (flushing) that undermines treatment compliance. In addition, high-dose treatment is required presumably owing to the poor pharmacokinetic properties of NA. The identification of the high-affinity NA receptor, namely G-protein coupled receptor 109A (GPR109A), led to further understanding of the pharmacological effects of NA and discovery of compounds that are potentially superior in efficacy yet devoid of NA's adverse effects.

OBJECTIVE/METHOD

This review focuses on the endeavors of several pharmaceutical companies to discover and develop GPR109A agonists. Representative compounds of each series in patent literature since 2005 are highlighted.

CONCLUSION

Highly potent GPR109A agonists with minimal flushing effects and robust free fatty acid reduction have been identified. Despite the failure of the partial agonist MK-0354 to achieve efficacy in a Phase II clinical trial, at least three other GPR109A agonists have been evaluated in clinical trials. The upcoming clinical data would be critical to validate the therapeutic utility of this receptor.

[Role of LDL in cardiovascular diseases. New data and new recommendations]

The management of hypercholesterolemia has rapidly progressed with the large clinical trials mainly on statins. Over the past 15 years, it has been demonstrated that the principle target was LDL-cholesterol and that treatment with statins decreased cardiovascular morbidity and global mortality. The studies have progressively targeted patients with increasingly lower cholesterol levels but always at high risk. Recent data are in favour of the so-called "aggressive" strategy aimed at reducing cholesterol to very low levels. The emergence of new therapies with stronger statins and the concept of combining lipid-lowering treatments has improved the chances of reaching this aim. Prompted by this progress, the transposition of this aggressive strategy to clinical practice is confronted with many problems, which stem from practitioners' and patients' reticence and fears (raising the question of compliance to treatment) and, more generally, the problem of cost. In this perspective, therapeutic education is one of the tools that would promote compliance. New treatments in the field of HDL would further support the progress made in such prevention.

New drugs for the treatment of hypercholesterolaemia

Endogenous and exogenous pathways determine plasma levels of cholesterol and lipoproteins. Plasma cholesterol levels and coronary heart disease risk can be reduced pharmacologically by decreasing cholesterol synthesis, increasing its elimination and/or reducing its absorption from the intestine. The more profound knowledge about cholesterol homeostasis has allowed the development of several lipid-lowering drugs with different mechanisms of action, with the purpose of reducing both morbidity and mortality associated with coronary heart disease. Two new and more potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), also called superstatins (rosuvastatin and pitavastatin), are being studied for their ability to improve lipid profiles. Rosuvastatin is a potent, hepato-selective and relatively hydrophilic statin with a low propensity for muscle toxicity and drug interactions. Pitavastatin is another statin with a high oral bioavailability and minimal propensity for cytochrome p450-mediated drug interactions. Rosuvastatin seems to be more potent than other available statins while pitavastatin presents with a similar potency to that of atorvastatin. Another promising approach for lowering total and low-density lipoprotein cholesterol levels is inhibition of cholesterol absorption. A wide variety of new agents with the capacity for inhibiting the intestinal cholesterol absorption is currently being investigated. Ezetimibe is a selective cholesterol absorption inhibitor whose clinical efficacy has been recently demonstrated both in monotherapy and in combination with other lipid-lowering drugs. Colesevelam, a new bile acid sequestrant, has shown a clinical efficacy similar to that of other resins, with minimal gastrointestinal side effects, improving tolerability and patient compliance. Other lipid-lowering drugs with the ability to act at the enterocyte level, such as avasimibe and implitapide, are currently being investigated in humans.

Lovastatin and beyond: the history of the HMG-CoA reductase inhibitors

In the 1950s and 1960s, it became apparent that elevated concentrations of plasma cholesterol were a major risk factor for the development of coronary heart disease, which led to the search for drugs that could reduce plasma cholesterol. One possibility was to reduce cholesterol biosynthesis, and the rate-limiting enzyme in the cholesterol biosynthetic pathway, 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase, was a natural target. Here, I describe the discovery and development of lovastatin--the first approved inhibitor of HMG-CoA reductase--and the clinical trials that have provided the evidence for the ability of drugs in this class to reduce the morbidity and mortality associated with cardiovascular disease.